kirkw,
Go and read over on this web site:
http://www.grtu.org/ It should answer most of your concern's and questions. By the way the FLOWS link has ton's of info regarding flow rates.
To help save you some time here are some of the highlight's in order to answer your ?'s:
1.) When will it be fishable?:
That depends on the Experience, Knowledge and Judgement of the individual and the Risk that person is willing to assume. The general guideines apply:
Flows above 550 cfs are unsafe to wade.
Flows between 300 to 550 cfs should be undertaken by only those who have experience wading swift water conditions. Preferrably, you will have knowledge of the river bottom and would have waded the area previously. Much of the river will still be too swift and too deep to wade safely. The potential for being swept off your feet is high.
Flows between 200 to 300 cfs can be undertaken by most experienced waders. There are still areas that may be too swift or deep to wade. Inexperienced waders will have to be aware.
Flows below 200 cfs have moderate current. A few areas may create fall down potential.
Flows below 100 cfs have slow current.
Remember the Guadalupe is a fast flowing river. A fast current can carry you away like a fly in molasses.
2.) When is it going to be fishable?:
The most significant predictor for flows below Canyon Dam is the lake elevation of Canyon Lake itself. Using the Canyon Lake Elevation link you can retrieve 'real time' lake elevations. If Canyon Lake elevation is:
908.9 and below, the lake is in conservation pool. Releases are low.
909.0 the release rate will match the greater: Spring Branch Gage, or 90 cfs.
909.1 and above, the lake is in flood, heavy releases are imminent.
3.) Will the larger trout survive?:
YES
On January 1, Canyon Lake exceeded 909 elevation which means that trout protective flows will commence on May 1 for the entire period through September 30th. This is vitally important to the trout fishery, and will create trout fishing and water recreational opportunities throughout the summer.